Reverse intaglio amethyst

Hello,

Although I have been cutting cabochons of various stones for years, I
have started relatively recently with gemstone carving. I found that
lapis was not too bad to deal with, but I was wondering about reverse
intaglio. Has anyone performed reverse intaglio with amethyst? I was
going to carve an old english “B” in the backside of the stone, but
leave the intaglio with the frosted look by using just the diamond
bits without further polishing in the recesses. The top would be a
polished regular cabochon, with the back other than the recesses also
polished. Does anyone have any advice? Is what I have planned a bad
idea in that the frosting will not show to good effect the letter?
Would it be better to polish the recesses?

Many thanks for your time.
Sincerely,
Seech